DE102009024885B4 - Method of manufacturing a fiber optic sensor and use thereof - Google Patents

Abstract

A method of making a fiber optic sensor (10) comprising the steps of: providing a fiber core (11) and a cladding (12) surrounding the fiber core (11); applying a protective layer (13) of electrically non-conductive material to the cladding (12), - applying a further coating (14) on the protective layer (13), wherein the further coating (14) comprises a layer composite of at least two layers, wherein an outer layer (15) of the further coating (14) is a metal layer in that the fiber-optic sensor (10) can be connected to a metallic carrier (40), wherein an inner layer (16) is provided between the outer layer (15) and the protective layer (13), which activates the protective layer (13) and wherein the outer layer (15) of the coating (14) has a thickness of 50 μm up to several millimeters, and - destroying the protective layer (13) by a temperature treatment, so that the Fiber core (11) with the surrounding jacket (12) of the further coating (14) is mechanically decoupled and the outer layer (15) of the further coating (14) forms a guide tube.

Description

The invention relates to a method for producing a fiber optic sensor having a fiber core, a cladding surrounding the fiber core and a protective layer applied to the cladding of an electrically non-conductive material, wherein a further coating is applied to the protective layer. Furthermore, the invention relates to a method for producing a system which comprises such a method for producing a fiber-optic sensor and to a use of a fiber-optic sensor produced by such a method.

While the fiber core and the cladding surrounding the fiber core (so-called fiber cladding) consist of silicon dioxide (SiO ₂ ), the protective layer (so-called coating) applied to the cladding is typically formed from polyimide or acrylate. Often, a known under the trade name ORMOCER polymer material is used. The protective layer serves to protect the fiber core and the jacket during operation of the fiber optic sensor and its handling.

Fiber-optic sensors can be mechanically destroyed very quickly by shearing at edges or by looping. In addition, there is the problem that due to the materials used in the protective layer, use at high temperatures is not possible. With a protective layer of acrylate, there is a temperature threshold at approx. 100 ° C. With a protective layer of polyimide and ORMOCER this is about 250 ° C. Exceeding the relevant temperature threshold, the protective layer applied to the jacket would be destroyed, which would give the risk of cracking of the fiber core at low mechanical stress or vibration.

The materials used for the protective layer continue to bring with it the disadvantage that it is difficult to apply the fiber optic sensor on a metallic support. When the fiber-optic sensor is bonded to the metallic carrier, the protective layer together with the metal forms a heterogeneous composite material. In order to improve the application of the fiber-optic sensor to a metallic carrier, it has already been proposed to provide a thin copper layer on the protective layer. The disadvantage of this is that the temperature resistance of the copper layer is not sufficiently high for typical operating conditions. Due to the small layer thickness, the mechanical connection with the metal carrier, e.g. by means of a solder joint, proved to be difficult.

Otherwise provided coatings on the protective layer aim at an improvement of the optical properties for signal transmission.

The US 5 745 611 A describes an optical fiber having a core, a cladding, a stress modulating carbon layer, a polyimide protective layer of an inner metal layer of a mixture of chromium, nickel and gold and an outer gold layer plated on the inner metal layer. The core has a diameter of 5 μm. The outer diameter of the fiber is between 90 and 110 microns.

From the US 4,621,896 A For example, an optical fiber comprising a core, a cladding, a silicon oxide substrate, a silicon layer, and an outer nickel layer is known.

The US 4 504 113 A relates to an optical fiber having a core, a cladding, a 0.5 μm thick metal oxide protective layer, a metal oxide or zirconium glass layer and an outer plastic or resin layer.

The US 4 609 437 A discloses an optical fiber having a core, a cladding, a 60 μm thick resin layer, a 0.2 μm thick silver layer, a 2 μm thick nickel layer, and a lead-tin alloy layer. The total thickness of the metal layers is 10 to 20 μm.

The US 5 642 455 A describes an optical fiber with a conventional glass fiber, a 5 μm thick polymer sheath, a thin silver-epoxy-copper layer and a 20 μm-thick outer magnetic nickel-iron layer.

From the US Pat. No. 6,876,785 B1 For example, a fiber optic sensor embedded in a metal structure is known which comprises an optical fiber having an approximately 1 μm thick titanium layer and a 0.3 to 2 mm thick outer metal layer.

The DE 35 41 733 C1 describes a fiber optic sensor arranged in a housing and connected via optical connectors to the housing associated optical connectors.

The US Pat. No. 6,343,173 B2 discloses a fiber assembly comprising a cladding and a core optical fiber, a cladding, and a 1 to 10 μm thick outer gold layer.

The EP 0 884 813 A1 relates to an optical fiber having a core, a cladding, a 50 to 70 μm thick acrylate protective layer and a 15 μm thick outer gold layer.

From the US 4 418 984 A For example, an optical fiber comprising a core, a cladding, two metal layers, and an outer plastic layer is known.

It is an object of the present invention to provide a method for producing a mechanically loadable fiber-optic sensor, which is suitable for temperature measurement, for example for measuring the temperature of a connectable to the fiber optic sensor carrier.

It is another object of the present invention to provide a method of manufacturing a system comprising such a method of manufacturing a fiber optic sensor, and an advantageous use of a fiber optic sensor manufactured by such a method.

These objects are achieved by a method having the features of claim 1 and a use having the features of claim 17. Advantageous embodiments will be apparent from the dependent claims.

In a method of manufacturing a fiber optic sensor, a fiber core and a cladding surrounding the fiber core are provided, and a protective layer of an electrically nonconductive material is applied to the cladding. On the protective layer, a further coating is applied. The further coating comprises a layer composite of at least two layers. In this case, an outer layer of the further coating is a metal layer, so that the fiber-optic sensor is attachable to a metallic carrier, wherein between the outer layer and the protective layer, an inner layer is provided, which has the protective layer activating properties. The outer layer of the coating has a thickness of 50 microns to several millimeters. The protective layer is destroyed by a temperature treatment, so that the fiber core is mechanically decoupled from the further coating with the surrounding jacket and the outer layer of the further coating forms a guide tube.

Activation in this context means that the application of another layer (the outer layer) to the protective layer is made possible, with no limit as to its thickness.

Further coating gives the fiber optic sensor ductile mechanical properties, allowing for robust deployment and easier handling during production of the fiber optic sensor. By the layer composite of the further coating of at least two layers, on the one hand, the connection to a metallic carrier can be ensured. In this case, the inner layer allows the application of the thicker, outer layer, whereby the connection process to a carrier, in particular of a metal, can be realized. On the other hand, a fiber optic sensor is provided which can be used non-destructively at high temperatures above a material-dependent temperature threshold. With a protective layer of acrylate, there is a temperature threshold at approx. 100 ° C. With a protective layer of polyimide and ORMOCER this is about 250 ° C.

It is expedient if the outer layer of the coating is a metal layer which is temperature-resistant at temperatures of more than 100 ° C., preferably of more than 300 ° C., and most preferably of more than 500 ° C. The further coating thereby enables the use of the sensor for measuring the temperature of a carrier at temperatures above 500 ° C, without losing the mechanical properties of the fiber optic sensor.

In order to ensure the connection of the fiber optic sensor on a metallic support, the outer layer of the coating has a thickness of 50 microns to several millimeters, in particular 50 microns to 1 mm, preferably 50 to 150 microns. As a result, there is sufficient material of the outer layer for producing a cohesive connection available. It is particularly expedient if the outer layer of the coating consists of galvanic nickel or copper, since in this way the desired high operating temperatures of more than 500 ° C and up to about 600 ° C can be achieved.

By contrast, the inner layer of the coating consists of a conductive material, in particular gold. It is sufficient if the inner layer has a thickness of about 1 micron. The pre-coating can be done for example by gold PVD (Physical Vapor Deposition). This can be realized, for example, with a subcontractor. Alternatively, the inner layer of the coating may be formed from a conductive ink. The use of a conductive ink is more cost effective compared to gold. Leitlack is also easier to apply. However, providing the inner layer of gold can produce a more even layer. If a conductive ink is used, the inner layer has a thickness of preferably 20 to 50 μm.

A sensor in which the inner layer consists of a conductive ink is further characterized by the fact that the fiber core is mechanically decoupled from the further coating with the surrounding jacket. The decoupling is through Dissolution of the protective layer effected under the action of temperature after the inner layer is applied to the protective layer. The protective properties of the protective layer are then no longer needed in a fiber optic sensor, since the mechanical protection is provided by the outer layer of the further coating.

In accordance with a further embodiment, the fiber-optic sensor is an intrinsic sensor in which the fiber core has changed optical properties in an active length section compared with the remaining length sections and in which the properties in the active longitudinal section can be changed under temperature and / or strain action further coating is provided at least in the region of the active length section. Conveniently, the further coating is applied over the entire length of the sensor. As a result, in addition to the already mentioned mechanical protection, the application to the carrier in a simple and flexible way possible.

A method of manufacturing a system includes fabricating a fiber optic sensor by a method of the type described above, and connecting the sensor to a support, particularly metal. The method is characterized in that the sensor is connected to the carrier by soldering, gluing, crimping or flame spraying. These types of connection are possible only because the outer layer of the further coating allows high operating temperatures due to their material properties and their thickness during processing, without being damaged.

The fiber optic sensor can be selectively connected to the carrier. As a result, a mechanical decoupling is effected between the fiber-optic sensor and the carrier, whereby a temperature measurement of the carrier by the fiber-optic sensor is possible. Alternatively, the fiber optic sensor may be connected to the carrier throughout at least along the active length portion. As a result, a solid, continuous connection between the sensor and the carrier is effected, whereby a power transmission through the protective layer is carried out on the fiber optic sensor. As a result, an elongation of the carrier can be detected, in particular if the inner layer of the coating comprises gold.

Optionally, the fiber optic sensor can be applied to a surface of the carrier or inserted into a groove of the carrier, which is optionally closed. In the latter case, the sensor can be galvanized, soldered or glued into the groove.

In the method of manufacturing a system of the type described above, the fiber optic sensor is connected to the carrier by one of the following methods: soldering; Flame spraying; Glue; To squeeze; Laser welding; EB welding; Eingalvanisieren; filling; Advanced Laser Materials Manufacturing (ALM).

A fiber-optic sensor manufactured according to a method described above can be used for measuring the temperature of a carrier connected to it in a temperature range up to 1000 ° C. A fiber optic sensor that is not manufactured by a method according to the invention can be used to measure the strain on the beam to which the sensor is mechanically connected.

• 1 einen faseroptischen Sensor in einem Querschnitt,
• 2 den faseroptischen Sensor in einem Längsschnitt,
• 3 ein System in einer Seitenansicht gemäß einer ersten Variante, und
• 4 ein System in einer Seitenansicht gemäß einer zweiten Variante.

The invention will be explained in more detail below with reference to the exemplary embodiments illustrated in the drawings. Show it:

• 1 a fiber optic sensor in a cross section,
• 2 the fiber optic sensor in a longitudinal section,
• 3 a system in a side view according to a first variant, and
• 4 a system in a side view according to a second variant.

A fiber optic sensor 10 like this in a cross-sectional view in 1 and in a longitudinal section in 2 is based on a conventional from the prior art fiber with a fiber core 11 , one the fiber core 11 surrounding coat 12 and one on the coat 12 applied protective layer 13 made of a non-conductive material. The coat surrounding the fiber core is also referred to as fiber cladding. The fiber core 11 and the coat 12 each consist of silicon dioxide SiO ₂ (quartz), wherein the fiber core 11 may be doped with impurities while the cladding is undoped. The on the coat 12 Applied protective layer is often designed as ORMOCER (Organic Modified Ceramics). ORMOCER is a trade name for a polymer and serves to protect the fiber core as well as the sheath during operation of the fiber optic sensor 10 and its handling.

The fiber core 11 is doped at the locations marked 17, with the doped sites forming "sensor mirrors". The areas labeled 17 in the fiber core extend within an active length range 20 , Outside the active length range (indicated by the reference numeral 21 ) points the fiber core 11 no such, in their optical Properties of altered optical areas. An overall length of the fiber optic sensor 10 is marked with 22. As a result, an intrinsic sensor (so-called. FBG - Fiber Bragg Grating) is formed, wherein the fiber properties can be influenced by external effects. The fiber core is thus the sensor itself. The optical sensor properties of the fiber core are identified by the "sensor mirrors" marked 17 11 changed, wherein the optical change by means of a phase mask or an interference pattern is written by a UV excimer laser. Such intrinsic fiber optic sensors are well known in the art and can be obtained as standard components from various companies.

On the protective layer 13 an electrically non-conductive material is another coating 14 Applied to an outer layer 15 and an inner layer 16 includes. The inner layer 16 is optionally a gold layer, which by a PVD (Physical Vapor Deposition) method, for example, in a thickness of 1 .mu.m to 5 .mu.m on the protective layer 13 is applied or Leitlackschicht, which is produced for example in a thickness of 20 to 50 microns. Although the latter has a more uneven surface, it is less expensive to implement. As a material of the outer layer 15 It is preferable to use nickel, which is applied to the inner layer in a galvanic process 16 is applied. The outer layer 15 is produced in a layer thickness of 50 to 150 microns.

The further coating 14 represents a robust, metallic layer construction, which provides a better composite of fiber optic sensor 10 and realize a particular metallic carrier. In particular, it is possible by further coating, the fiber optic sensor 10 by soldering, flame spraying or adhesives continuous or punctually along the fiber to connect with the carrier. In addition, the fiber optic sensor receives 10 through the further coating 14 Ductile mechanical properties, which allow a more robust use and easier handling during production. While conventional fiber optic sensors can be used depending on the material up to only 100 ° C (with a protective layer of acrylate) or 250 ° C (with a protective layer of polyimide and ORMOCER), a fiber optic sensor can be used even at higher temperatures. This allows a sensor measurement in the range of up to 1000 ° C, with the mechanical properties of the fiber optic sensor 10 however, continue to be preserved.

The described fiber optic sensor can, as in the embodiments of the 3 and 4 shown on a surface of a carrier 40 be upset. Alternatively, and not shown in the figures, the fiber optic sensor 10 in a groove of the carrier 40 be introduced, which is optionally closed. The sensor can 10 To be galvanized, soldered or glued into the groove. The connection of the fiber optic sensor to the carrier 10 can, depending on the use of the sensor 10 , punctually or continuously at least along the active length section 20 be realized. The fiber optic sensor 10 is here in such places of the carrier 40 attached, on which certain loads that the carrier is to endure, must be measured. If the fiber optic sensor 10 in a groove of the carrier 40 is introduced, the weakening of the carrier must be taken into account by the introduction of the groove in the interpretation. As in the embodiments of the 3 and 4 are shown at the opposite free ends of the fiber optic sensor 10 plug 30 attached, which via a respective connecting cable 31 can be connected to a meter.

A mechanical decoupling of the sensor 10 from the carrier 40 due to the only selective connection of sensor and carrier (see reference numeral 41 in 3 ) causes a shift of the "sensor mirrors" 17 in the fiber core with a temperature change 11 , This results in a change in the base wavelength of the (FBG) sensor. This allows the temperature of the wearer 40 be measured. This effect of mechanical decoupling can be used with a fiber optic sensor because the protective layer 13 is dissolved. This resolution is achieved by exposing the fiber-optic sensor, for example during its production, to such a high temperature that results in a resolution of the protective layer 13 leads. The outer layer acts here 15 the further coating 14 then as mechanical protection by forming a "guide tube".

In contrast, in the case of a fixed connection (cf. 42 in 4 ) between the sensor 10 and the carrier 40 Strains of the wearer on the "sensor mirror" 17 go over, whereby a strain measurement is possible. This is possible in a comparative example, which is not the subject of the invention, for those temperatures which are the protective layer 13 do not destroy, causing the protective layer 13 an elongation on the fiber core 11 can transfer.

Depending on the intended use of the fiber optic sensor - temperature measurement or strain measurement - the following structure of the sensor or the following procedure is provided.

Temperature measurement:

The fiber core 11 , Coat 12 and protective layer 13 formed arrangement is made with the conductive ink or gold as the inner layer 16 coated. The coating takes place at least along the active length section 20 and typically over the entire length of the fiber optic sensor 10 , The inner layer 16 serves to activate the underlying protective layer 13 , This can ensure that in a subsequent galvanic process, the application of the outer layer 15 made of nickel is possible. In order to carry out the temperature measurement in areas up to 1000 ° C, a targeted destruction of the protective layer 13 performed by a high temperature treatment of over 300 ° C. The protective function of the fiber core 11 and the surrounding jacket 12 gets through the outer layer 15 provided.

Comparative Example - Strain Measurement (not the subject of the invention):

The fiber core 11 , Coat 12 and protective layer 13 existing arrangement is provided with a layer of gold. The coating takes place at least along the active length section and typically over the entire length of the fiber optic sensor.

If the strain measurement is carried out in a temperature range of less than 250 ° C, then the further coating 14 directly on the protective layer 13 applied. The fiber prepared in this way can be soldered to the carrier, for example 40 be applied. This results in a good connection to the carrier and thus a good transmission behavior with respect to the elongation of the carrier in the fiber optic sensor.

If the strain measurement takes place at temperatures above 300 ° C, then the further coating 14 , In particular, the layer of gold, rather than on the protective layer 13 also directly on the coat 12 be applied. The thus prepared fiber is also fixed by soldering on the carrier. Since evaporation of the protective layer does not occur due to its non-existence, a good connection between the fiber-optic sensor and the carrier is also achieved here.

LIST OF REFERENCE NUMBERS

10

Fiber optic sensor

11

fiber core

12

Coat (cladding)

13

Protective layer (ORMOCER)

14

additional coating

15

outer layer

16

inner layer

17

"Sensorspiegelchen"

20

active length section

21

remaining length section

22

Overall length of the fiber optic sensor

30

plug

31

electric wire

40

carrier

41

selective connection

42

continuous connection

Claims (17)

Method for producing a fiber-optic sensor (10) with the steps: Providing a fiber core (11) and a jacket (12) surrounding the fiber core (11), Applying a protective layer (13) of an electrically non-conductive material to the jacket (12), - Applying a further coating (14) on the protective layer (13), wherein the further coating (14) comprises a layer composite of at least two layers, wherein an outer layer (15) of the further coating (14) is a metal layer, so that fiber optic sensor (10) to a metallic support (40) is attachable, wherein between the outer layer (15) and the protective layer (13) an inner layer (16) is provided, which has the protective layer (13) activating properties, and wherein the outer layer (15) of the coating (14) has a thickness of 50 μm to several millimeters, and - Destroy the protective layer (13) by a temperature treatment, so that the fiber core (11) with the surrounding jacket (12) of the further coating (14) is mechanically decoupled and the outer layer (15) of the further coating (14) Forms guide tube. Method according to Claim 1 , characterized in that the protective layer (13) is destroyed by a temperature treatment at a temperature of about 300 ° C. Method according to Claim 1 , characterized in that the outer layer (15) of the coating (14) has a thickness of 50 microns to 1 mm. Method according to Claim 1 or 2 , characterized in that the outer layer (15) of the coating (14) has a thickness of 50 to 150 microns. Method according to one of Claims 1 to 3 , characterized in that the outer layer (15) of the coating (14) is a metal layer which is temperature resistant at temperatures of more than 300 ° C. Method according to one of Claims 1 to 4 , characterized in that the outer layer (15) of the coating (14) is a metal layer which is temperature resistant at temperatures greater than 500 ° C. Method according to one of the preceding claims, characterized in that the outer layer (15) of the coating (14) consists of galvanic nickel or copper and / or that the inner layer (16) of the coating (14) consists of a conductive material. Method according to one of the preceding claims, characterized in that the inner layer (16) of the coating (14) consists of gold. Method according to one of the preceding claims, characterized in that the inner layer (16) has a thickness of 1 to 5 microns and / or that the existing inner gold layer (16) by a PVD method applied to the protective layer (13) becomes. Method according to one of Claims 1 to 6 , characterized in that the inner layer (16) of the coating (14) consists of a Leitlack and / or that the inner layer (16) has a thickness of 20 to 50 microns. Method according to one of the preceding claims, characterized in that the fiber-optic sensor (10) is an intrinsic sensor, in which the fiber core (11) in an active longitudinal section (20) relative to the remaining length sections (21) defines and has changed optical properties in which the properties in the active longitudinal section (20) are variable under the influence of temperature, wherein the further coating (14) is provided at least in the region of the active longitudinal section (20). A method of manufacturing a system comprising the steps of: - producing a fiber optic sensor (10) according to a method according to any one of Claims 1 to 11 and - bonding the sensor (10) to a substrate (40) by soldering, gluing, flame spraying, laser welding, EB welding, plating, backfilling or Advanced Laser Materials Manufacturing (ALM). Method according to Claim 12 , characterized in that the carrier (40) consists of metal. Method according to Claim 12 , characterized in that the fiber optic sensor (10) is selectively connected to the carrier (40) or that the fiber optic sensor (10) is connected to the carrier (40) continuously at least along the active length portion (20). Method according to one of Claims 12 to 14 , characterized in that the fiber optic sensor (10) is applied to a surface of the carrier (40) or that the fiber optic sensor (10) is introduced into a groove of the carrier (40). Method according to Claim 15 , characterized in that the groove of the carrier (40) is closed. Use of a method according to any one of Claims 1 to 11 manufactured fiber-optic sensor (10) for temperature measurement of a support (40) to which the sensor (10) is mechanically connected, in a temperature range up to 1000 ° C.

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